Electrolytic Conductance, Electrolysis, Batteries and Corrosion — Part 2: Electrolysis, cells and corrosion: visual lesson, ISC Class 12 Chemistry

Lesson

Electricity making chemicals, chemicals making electricity

Part 2 — electrolysis, batteries, fuel cells and the corrosion of iron.

In this lesson you will

State and apply Faraday’s first and second laws of electrolysis, and relate the faraday to Avogadro’s number and the electronic charge
Write electrode reactions for the dry cell, mercury cell, lead storage battery and hydrogen–oxygen fuel cell
Distinguish primary from secondary cells
Explain rusting as an electrochemical process and describe methods of preventing corrosion

Diagram

Electrolysis

In an electrolytic cell a battery pushes electrons into the cathode, where cations are reduced, and draws them from the anode, where anions (or the anode metal) are oxidised.

Concept

Faraday’s laws of electrolysis

First law: the mass of a substance deposited or liberated at an electrode is proportional to the quantity of electricity passed: $m = ZQ = ZIt$ , where $Z$ is the electrochemical equivalent. Second law: when the same quantity of electricity passes through different electrolytes, the masses of substances deposited are proportional to their equivalent masses: $\dfrac{m_1}{m_2} = \dfrac{E_1}{E_2}$ .

m = ZIt = \frac{E\,It}{F} = \frac{M\,It}{nF}

\frac{m_1}{m_2} = \frac{E_1}{E_2}

Table of faradays required and equivalent masses for some electrode reactions
Electrode reaction	Faradays per mole of product	Equivalent mass
Ag⁺ + e⁻ → Ag	1	108
Cu²⁺ + 2e⁻ → Cu	2	31.75
Al³⁺ + 3e⁻ → Al	3	9
2H⁺ + 2e⁻ → H₂	2 (per mol H₂)	1

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